1. Field of the Invention
The invention relates to a process of reactivating catalysts. In particular, it relates to the reactivation of noble metal-causing zeolite catalysts which have been deactivated by coke build-up. Catalysts which may be reactivated by the process of the present invention include those that have become deactivated during hydrocarbon hydroprocesses, such as the reforming or catalytic dewaxing of hydrocarbon feedstocks.
2. Discussion of the Prior Art
Reactivation of platinum catalysts utilized in hydrocarbon hydroprocessing procedures such as reforming is known in the art. Processes which utilize chlorine and oxygen in catalyst reactivation are particularly well-known. For example, U.S. Pat. No. 2,906,702 to Brennan et al discloses a method of restoring an alumina-supported platinum catalyst after deactivation occurring during the reforming of hydrocarbons. This method teaches contacting a deactivated platinum-alumina catalyst with a gaseous chlorine, fluorine, or other halogen or halogen-affording substance at an elevated temperature. U.S. Pat. No. 3,134,732 to Kearby et al teaches a method for reactivating noble metal catalyst supported on alumina by contacting the catalyst with halogen-containing gas, stripping excess halogen therefrom, and subjecting the resulting catalyst to a reduction step with a hydrogen-containing gas. In this disclosure, the agglomerated metal is present on the surface of the alumina as small crystallites. It is also known in the art to regenerate noble metal- and platinum group metal-containing zeolite catalysts. Regeneration of noble metal-loaded zeolite catalysts required certain procedural modifications to regain the activity of the metal. U.S. Pat. No. 3,986,982 to Crowson et al treats deactivated platinum group metal-loaded zeolites by contacting them with a stream of an inert gas containing from 0.5 to 20 percent volume of free oxygen and from 5 to 500 ppm volume of chlorine as chlorine, HCl, or an organic chlorine-containing material. The resulting catalyst is purged to remove residual oxygen and chlorine and then reduced in a stream of hydrogen at 200.degree. to 600.degree. C.
The treatment of noble metal-containing catalyst material with sulfur compounds is also known in the art. For example, U.S. Pat. No. 3,661,768 to Davis, Jr., et al. describe a method of regenerating a bimetallic reforming catalyst such as platinum-rhenium on alumina which includes contacting the catalyst with hydrogen sulfide to convert platinum to platinum sulfide. Prior to sulfiding, the catalyst is contacted with chlorine and steam in order to effect chlorination.
However, all of the above treatments require certain precautions owing to the corrosive nature of the halogens ued. In addition, certain halogen materials employed in these processes add significantly to the cost of catalyst regeneration. In order to avoid the drawbacks associated with halogen use, it would be advantageous to reactivate catalysts in the absence of halogens. However, when deactivating coke present on a catalyst material is exposed to an oxidizing atmosphere consisting of oxygen and an inert gas, such as nitrogen, substantially all of the noble metal present on the catalyst becomes catalytically inactive.